They sell for $9.99 in stores, but there’s a $10 credit that every buyer can redeem back to their bank account. Square has a store locator here where customers can find out where to buy Square units.

Overall, the business has three legs right now. They’ve got the readers, which work with the iPhone, Android devices and iPads. Then they’ve got an iPad app called Register. Lastly, there’s Pay With Square, which is an app that people can use at their favorite local shops to pay by merely saying their name to the cashier at the register.

The readers, along with Square’s other products, are now handling transactions at an annual rate of about $5 billion per year with more than 1 million registered customers. Given Square’s main transaction rate of 2.75 percent, a back-of-the-envelope calculation suggests the company is grossing nearly $140 million in revenue on an annualized basis. But remember that most of that fee goes back to credit card companies like Visa and Mastercard, so net revenue would be much lower.

We’ve also heard that Square is still in the process of raising $250 million at a $4 billion valuation and has pitched institutional investors like Legg Mason and Fidelity. That hasn’t been confirmed yet but stay tuned. Hopefully, the dismal performance of Facebook’s shares after the company’s IPO hasn’t scared institutional investors off of late-stage, growth rounds.